1. Field of the Invention
This invention relates to motor driven pumps.
2. Description of the Prior Art
Many designs of motor driven pumps have heretofore been proposed among which are those shown in U.S. patents to White, U.S. Pat. Nos. 2,713,311, 2,741,990, 2,763,214, 2,796,835, 2,906,208, 2,913,988, 3,053,189, 3,111,000, 3,138,105, 3,220,349, 3,220,350 and 3,280,750 and Litzenberg, U.S. Pat. No. 2,871,791.
It has been common practice in motor driven pumps in which the motor rotor and motor stator are isolated by a sleeve to support the outer end bearing of the motor rotor either by the use of a heavy casing or to rely upon the isolating sleeve in the stator to provide such support. Problems have arisen in the designs heretofore available of obtaining and maintaining alignment of the motor stator, and the motor rotor, and particularly of the end of the shaft remote from the impeller.
It has been difficult with the motor driven pumps heretofore available to achieve and maintain the desired tolerances and minimum clearances, including that at the air gap between the motor rotor and its isolating sleeve, and to provide part interchangeability with the desired tolerances and clearances.
It has also heretofore been propsed to provide simple suction inlet centrifugal motor driven pumps utilizing two orifices, one fixed and one variable, for providing a pressure effective on the rotor assembly to balance the pressure developed on the impeller. None of the structures heretofore proposed have proven wholly satisfactory in practice for various reasons.
White, in U.S. Pat. No. 3,138,105 shows a motor driven pump which has a hollow rotating shaft and a plurality of fixed orifices including grooves 55a of the bearing block 54, the clearances between the shaft 60 and the face of bearing 58 at the left of FIG. 1, the grooves 57a, the clearance between the motor rotor enclosure 67 and the sleeve 30, the clearance between the shaft 60 and the face of the bearing 58 at the right of FIG. 1. The multiplicity of fixed orifices in series, the separate streams with variation of pressure drops with change of developed pressure results in an ineffectual structure which has no standard pressure drop or flow limitation for utilization at the variable orifice between the end face 64 and the inner surface of the sleeve end closure plate 32. The structure disclosed in this White patent also lacks the advantages in manufacture of the pump of the present invention.
White, in U.S. Pat. No. 3,220,349, shows a motor driven pump which has a hollow rotating shaft and a wearing ring on the impeller to create a pressure drop and a variable orifice intended to provide the balancing pressure. A wearing ring is non-compensating due to the variation of its pressure drop with wear, change of length and change of diameter.
This patent, in addition to the wearing ring has three other fixed orifices at the ports 36, the gap between the enclosure 40 of the motor rotor and the sleeve 25, and the grooves in the bearing 33 at both sides of motor rotor. The variable orifice 55 is called upon to function with three fixed orifices which are widely diverse in design and pressure drops. The variable orifice 55 at shut off point when it contacts the back face of the impeller will have wear contact due to axial thrust and will not function properly after normal wear occurs.
The multiplicity of fixed orifices, planned or unplanned, results in a lack of a standard or measurable fixed orifice for operation with a variable orifice, with resultant incapability of automatic accommodation to all the variables of impeller diameters, speeds, and specific gravities or viscosities of the fluid being pumped.
White, in U.S. Pat. No. 3,280,750, shows a motor driven pump with orifices providing flame traps for explosion proof uses. A rotating shaft is employed. A wearing ring is provided for controlling pressures on portions of the impeller but is restricted to a single size of impeller diameter. Four fixed orifices are shown, one at 36 which is a flame trap which can clog, the gap 40 between the impeller enclosure and the isolating sleeve, the bearing passageway 40 and the flame path 49. The limit on clearances is stated as not to exceed 0.0036 inch. The restriction on the flame path 49 used as a variable orifice so severely restricts the flow as to make it unreliable for achieving axial thrust balance.
This structure, with its multiplicity of orifices and limitations on its effectiveness is subject to the same shortcomings as those of the White patents previously referred to.
Pezzillo, in U.S. Pat. No. 3,288,073, shows a canned pump intended to have reduced hydraulic thrust. Pezzillo has a hollow rotating shaft with axial thrust washer and bearings described as in contact at all times so that no "floating" shaft would be available.
Pezzillo, like the White patents previously referred to, does not have any available standard fixed orifice for operation with a variable orifice with resultant incapability of automatic accommodation to variables which are inescapable in pump design and operation.
A simplified motor driven pump is provided which overcomes many of the shortcomings of the motor driven pumps heretofore available, particularly as to pressure balancing of the impeller and motor rotor.